Spectroscopic temperature measurements in oxygen discharges

The rotational temperature of the excited state O 2 (b 1 Sigma g + , v=0) in an oxygen glow discharge is measured from the intensity distribution of the atmospheric A-band O 2 (b 1 Sigma g + , v=0) to O 2 (X 3 Sigma g - , v=0) at lambda =760 nm. The kinetic temperature, often called the gas temperature is also deduced using vacuum ultraviolet absorption spectroscopy in the same experimental conditions: pressure p=0.5-5 torr, discharge current up to 100 mA and deposited power up to 2 W cm -1 . It is shown that the rotational temperature of the A-band is equal to the rotational temperature of the molecular X 3 Sigma g - ground state and of the first metastable as 1 Delta state measured by coherent anti-Stokes Raman spectroscopy. Since the kinetic temperature is in equilibrium with the rotational temperature of the ground state, we conclude that the rotational temperature of the O 2 (b 1 Sigma g + ) state is identical to the gas temperature.